In the clotting of blood, the .alpha.- and .beta.-chains of blood protein fibrinogen is cleaved at the Arg-Gly (arginyl glycine) bonds by the enzyme thrombin, producing fibrin which polymerizes and is subsequently crosslinked enzymatically to form a permanent blood clot. The art suggests that the specificity of the thrombin-fibrinogen reaction is attributable to the amino acid sequence of the .alpha.- and .beta.-chains of fibrinogen, particularly in the vicinity of the Arg-Gly bonds. In the synthesis of the 14-22 sequence of the .alpha.(A) chain of human fibrinogen for study of its activity, i.e., binding and cleavage, toward the enzyme thrombin, analogs and fragments of this nonapeptide were synthesized in order to assess how activity toward thrombin would vary with change or alteration of structure.